1. Field of the Invention
The present invention relates to a magnetoresistive material whose electric resistance is altered responsive to a variation of a magnetic field externally produced.
2. Prior Art
Conventionally, there are provided magnetoresistive materials whose electric resistance is altered responsive to the variation of the magnetic field externally produced. Such effect of the magnetoresistive materials is called "magnetoresistive effect" (or simply called as "MR effect"). The above-mentioned magnetoresistive materials are widely used, in the magnetic recording/reproducing apparatuses, for the magnetic heads, sensors which sense the magnetic field, and the like. The known alloyed-magnetoresistive materials such as the Ni--Fe alloy (i.e., Permalloy) are used as the magnetoresistive materials. In addition, the granular-type magnetoresistive materials, which have fine magnetic granules embedded in the conductive non-magnetic metals, are also known. According to the known granular-type magnetoresistive materials, cobalt (Co) is embedded in copper (Cu); cobalt (Co) is embedded in silver (Ag); or Fe--Co alloy is embedded in silver (Ag), for example.
However, the known magnetoresistive materials described above suffer from the following drawbacks.
In the alloyed-magnetoresistive materials such as the Permalloy, the saturation magnetization is relatively large. Thus, when being applied to the magnetic head or sensor, the width of the magnetoresistive member (i.e., width of the magnetoresistive wire) should be reduced in order to improve the resolution. In that case, the effect of the demagnetizing field becomes large, which results in the reduction of the sensitivity for the detection of the magnetic filed. This phenomenon can be explained in detail by referring to FIGS. 7A and 7B. In those drawings, there is provided a magnetoresistive member 10 to which the magnetic anisotropy is imparted in its longitudinal direction. Under the condition where electric currents are applied to the magnetoresistive member 10 along longitudinal direction, an external magnetic field `Hex`, which is crossing the magnetoresistive member 10 in a direction perpendicular to the longitudinal direction, can be detected. In this case, as shown in FIG. 7B, magnetization M, which is caused due to the external magnetic field Hex in the magnetoresistive member 10, acts as demagnetizing field lid which is produced in a direction inverse to the direction of the external magnetic field Hex. Thus, the external magnetic field Hex is weakened by the demagnetizing field Hd. As a result, the sensitivity of the magnetoresistive member 10 for the detection of the magnetic field is reduced. On the other hand, the granular-type magnetoresistive materials are advantageous in that the saturation magnetization is relatively small. In other words, the granular-type magnetoresistive materials are hardly affected by the demagnetizing field. Thus, even if a width of a strip of the magnetoresistive member is narrowed, the sensitivity may not be substantially reduced. Actually, however, the granular-type magnetoresistive materials is not suitable for the practical usage, because the absolute sensitivity for the detection of the magnetic field is low.